We are attempting to understand molecular events in animal cell chemotaxis. We have studied migratory behavior in both phagocytic cells and a number of other differentiated cells that synthesize and remodel biological matrices. A partially purified tumor-derived antileukotactic factor may exert its effect by decreasing cell adherence and the formation of toxic 02 species. The active material may be an ester. Processing the chemotactic signal in leukocytes may involve the inactivation (by phosphorylation) of a protein which inhibits phospholipase A2, an enzyme required for chemotaxis. Studies on leukocyte adherence, a principal requirement for chemotaxis, show that these cells may use laminin as an attachment factor. Fibroblasts are attracted to certain growth factors and materials from fibrotic tumors. Endothelial cells respond to materials from tumors that also contain angiogenic activity. These findings are relevant to mechanisms of tumor survival. Bone cells are attracted to materials from demineralized bone, powder, suggesting a role for chemotaxis in bone induction.